The ability to clear pathogens is critical to survival. During evolution, two defense strategies to deal with microorganisms have developed: the innate and the aquired immune systems. Drosophila is a perfect model system to study innate immunity. It is genetically manipulable and several pathways involved in mammalian immune functions are highly conserved and activated in response to immune challenge. The immune response to pathogens in Drosophila leads to the appearance of "melanotic tumors" that are the result of blood cell encapsulation of pathogens. Melanotic tumors can also be caused by an autoimmune response or hyperproliferation of blood cells. Therefore, the goals of this proposal are. 1) to conduct a genetic screen for mutations associated with melanotic tumors. 2) characterize the mutants phenotypically and genetically. In particular their effects on NFkB, Jak/Stat, and Jnk signalling will be analyzed. 3) to clone mutants isolated in the screen. We will identify genes involved in both immunity and growth control.